Unfortunately, that part is only accessible via templates and not on the editor on the admin. To add contents on the right side, below or above those tags, per portfolio item, it needs customization of the template. I can see you don't have a child theme yet. Please see this:
Then copy content-portfolio.php from this folder \wp-content\themes\x\framework\views\integrity to your child theme here: \wp-content\themes\x-child\framework\views\integrity. Then edit the template as intended.
Hope this helps.